Existing .eth domain holders will remain able to renew their names during and after the transition to ENSv2.

From the articleEthereum Name Service Seeks DAO Approval for ENSv2 Rollout on Ethereum MainnetAlso in Ethereum Name Service plans major .eth overhaul with one irreversible catch for domain holders, ENS seeks approval for major .eth domain upgrade, ENS DAO Asked to Approve ENSv2 Activation Proposal, ENS Proposes Moving Ethereum Domain Registrations to Upgraded System